U.S. patent application number 16/569243 was filed with the patent office on 2020-01-02 for infrared band pass system for optical detection of parameters.
This patent application is currently assigned to Schott Glass Technologies (Suzhou) Co. Ltd.. The applicant listed for this patent is Schott Glass Technologies (Suzhou) Co. Ltd.. Invention is credited to Kazuyuki Inoguchi.
Application Number | 20200007795 16/569243 |
Document ID | / |
Family ID | 59396977 |
Filed Date | 2020-01-02 |
United States Patent
Application |
20200007795 |
Kind Code |
A1 |
Inoguchi; Kazuyuki |
January 2, 2020 |
INFRARED BAND PASS SYSTEM FOR OPTICAL DETECTION OF PARAMETERS
Abstract
A glass substrate having an average thickness of the glass
substrate from 0.01 to 1.2 mm and having a temperature dependence
of refractive index at a wave-length of 850 nm in a temperature
range from -40.degree. C. to 60.degree. C. of not more than
10.times.10.sup.-6/K.
Inventors: |
Inoguchi; Kazuyuki; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schott Glass Technologies (Suzhou) Co. Ltd. |
Jiangsu |
|
CN |
|
|
Assignee: |
Schott Glass Technologies (Suzhou)
Co. Ltd.
Jiangsu
CN
|
Family ID: |
59396977 |
Appl. No.: |
16/569243 |
Filed: |
September 12, 2019 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
16045288 |
Jul 25, 2018 |
10455167 |
|
|
16569243 |
|
|
|
|
PCT/CN2016/072044 |
Jan 25, 2016 |
|
|
|
16045288 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06K 9/00597 20130101;
G06F 21/32 20130101; H04L 63/0861 20130101; G02B 5/208 20130101;
G02B 5/285 20130101; H04N 9/04 20130101; H04W 12/06 20130101; G07C
9/37 20200101; H04N 5/33 20130101 |
International
Class: |
H04N 5/33 20060101
H04N005/33; G06F 21/32 20060101 G06F021/32; G06K 9/00 20060101
G06K009/00; H04L 29/06 20060101 H04L029/06 |
Claims
1. A glass substrate having an average thickness of the glass
substrate from 0.01 to 1.2 mm and having a temperature dependence
of refractive index at a wave-length of 850 nm in a temperature
range from -40.degree. C. to 60.degree. C. of not more than
10.times.10.sup.-6/K.
2. The glass substrate according to claim 1, wherein the glass
substrate has a transmission of more than 90% at a 10 mm thickness
in a wavelength region of 780 to 1,000 nm.
3. The glass substrate according to claim 1, wherein the glass
substrate has a Knoop hardness HK0.1/20 of more than 450.
4. The glass substrate according to claim 1, wherein an average
thickness of the glass substrate is 0.1 to 0.7 mm.
5. The glass substrate according to claim 1, wherein the glass
substrate is produced by a drawing process.
6. The glass substrate according to claim 1, wherein the glass
substrate is produced by a float process.
7. An infrared band pass filter, comprising: a glass substrate; and
at least one coating applied to the glass substrate, the glass
substrate having a thickness of 0.01 to 2 mm, the glass substrate
having a temperature dependence of refractive index at a wavelength
of 850 nm in a temperature range from -40.degree. C. to 60.degree.
C. of not more than 10.times.10.sup.-6/K, and the at least one
coating having a thickness of not more than 0.5 mm.
8. The infrared band pass filter according to claim 7, wherein the
band pass filter has a passband in a wavelength region of from 780
nm to 1,000 nm.
9. The infrared band pass filter according to claim 8, wherein the
band pass filter has a passband in a wavelength region of from 800
nm to 900 nm.
10. The infrared band pass filter according to claim 7, wherein a
temperature dependence of refractive index of the at least one
coating is less than 0.001/K.
11. The infrared band pass filter according to claim 7, wherein a
ratio of the temperature dependence of refractive index of the
coating to the temperature dependence of refractive index of the
glass substrate does not exceed 1,000.
12. The infrared band pass filter according to claim 7, wherein the
coating has from 10 to 1,000 layers.
13. The infrared band pass filter according to claim 7, wherein the
at least one coating is formed by physical vapor deposition.
14. The infrared band pass filter according to claim 7, wherein the
at least one coating is formed by a sol-gel process.
15. The infrared band pass filter according to claim 7, wherein
coating materials are selected from Nb.sub.2O.sub.5, TiO.sub.2,
Ta.sub.2O.sub.5, SiO.sub.2, MgF.sub.2, Al.sub.2O.sub.3, HfO.sub.2
and ZnO.sub.2.
16. An infrared band pass filter, comprising: a glass substrate;
and at least one coating formed on the glass substrate, the glass
substrate having a thickness of 0.01 to 2 mm, the at least one
coating having a thickness of not more than 0.5 mm, and a
temperature dependent center wavelength drift in the filter is less
than 15 nm in a temperature range from -40.degree. C. to 60.degree.
C.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a division of U.S. patent application Ser. No.
16/045,288, entitled "SYSTEM FOR OPTICAL DETECTION OF PARAMETERS",
filed Jul. 25, 2018, which is incorporated herein by reference.
U.S. application Ser. No. 16/045,288 is a continuation of PCT
application No. PCT/CN2016/072044, entitled "SYSTEM FOR OPTICAL
DETECTION OF PARAMETERS", filed Jan. 25, 2016, which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] This invention relates to a parameter detection system, an
infrared band pass filter, and a glass substrate for the infrared
band pass filter as well as a method for detecting parameters.
2. Description of the Related Art
[0003] A parameter detection system as described above can for
example be used for detecting parameters in individuals, such as
iris recognition, 3D scanning, touch sensors, biometrics,
interactive displays, gaming and gesture control.
[0004] In the sense of this invention a "parameter detection
system" is a typically electronic system that is capable of
measuring at least one parameter of at least one individual or
object. The parameter that is measured can be selected from any
parameters that can be measured using optical means. "Detection"
includes qualification and/or quantification of the respective
parameter.
2. Description of the Related Art
[0005] Gesture control devices, iris scanners and other related
parameter detection devices are as such known from the prior art.
These devices typically comprise an infrared light source for
illuminating the area to be detected ("illumination unit"). The
wavelength irradiated by the light source typically is in the area
of from 800 to 900 nm. In order to capture infrared light that is
coming back from the area to be detected, e.g. the person who uses
the device, it is preferable that only the wavelength of light
which carries the useful information is measured. Measuring only
the desired wavelength and filtering out other ranges of the
wavelength spectrum, increases the signal-to-noise (S/N) ratio and
allows the illuminating light intensity to be decreased. For this
purpose infrared band pass filters are used that have good
transmission in the desired wavelength regions. The wavelength
region that passes the filter is called "passband region".
[0006] The reason why infrared light is used to illuminate the
scene is that the S/N ratio can be improved, in particular in
environments with high brightness in the visible wavelength
range.
[0007] Other components that may be used in such a device are a
lens that gathers the light reflected from the scene and an image
sensor such as a time-of-flight camera. The image sensor measures
the time the light has taken to travel from the illumination unit
to the detected object and back. Thus, the devices usually comprise
an illumination device, a band pass filter, and an image
sensor.
[0008] WO 2013/010127 A2 teaches biometric imaging devices and
methods. The systems described therein contain a light source and
an imaging device. An infrared transparent medium can be used to
conceal the imaging device from the individual. The infrared
transparent medium can be made of glass or plastic and it can
include a coating. The document focuses on the semiconductor device
used in the imaging device. The imaging device may also include an
infrared filter. No further details are discussed.
[0009] U.S. Pat. No. 8,750,577 B2 discloses a method and apparatus
for eye-scan authentication using a liquid lens. US 2013/0227678 A1
relates to a method and system for authenticating a user of a
mobile device. A lot of different configurations for detection
systems of biometric data and other parameters have been published.
However, little emphasis has been put on optimizing band pass
filters for use in such devices.
[0010] Different substrates can be used for infrared band pass
filters. Each substrate has certain properties and a benefit in one
property may be accompanied by a drawback regarding another
property of the substrate. Most band pass filters comprise a
substrate and one or more coatings. Some of the properties that
such a filter should have are the following: [0011] high
transmission in the passband region; [0012] very low transmission
in the block region; [0013] scratch resistance; [0014] resistance
to breakage even at low thickness; [0015] good chemical stability,
e.g. hydrolytical stability; [0016] compatible thermal expansion;
[0017] optimized optical properties; [0018] low angle dependency of
optical properties; [0019] low content of environmentally harmful
or toxic components; [0020] low specific weight; [0021] low
radiation (fluorescence, phosphorescence, radioactivity); [0022]
low manufacturing costs; [0023] availability in low thicknesses and
with low thickness variance; and [0024] thermal shock
resistance.
[0025] High transmission at the desired wavelength is of particular
relevance because light intensity cannot be increased to very high
values. Light of very high intensity will damage the user's tissue,
in particular in iris recognition systems. Also, illuminating the
scene with high light intensities requires a lot of energy.
[0026] Many parameter detection systems are useful in portable
devices such as mobile phones and tablet or laptop computers.
Portable devices are subject to variations in ambient temperature.
For example, a mobile device should work not only indoors but also
when being used outside. During outdoor activities (such as skiing)
very cold temperatures may affect the device. Also, very hot
temperatures may occur in situations when a device is in direct sun
light. Generally, the temperature range within which a portable
electronic device or a device for outdoor use in general should
work properly is roughly from -40.degree. C. to 60.degree. C., i.e.
in a temperature range of about 100.degree. C. It has been found
that this is not a self-evident property in many materials.
[0027] It has been found that the optical properties should not
only be good for the desired application but the optical properties
should also remain as constant as possible over the indicated
temperature range. While transmission does usually not vary very
much with changing temperature, the refractive index varies to a
significant extent with changing temperatures. Even this may not be
very problematic in certain optical systems, but when it comes to
coated systems, the refractive index change causes a change in
transmission as well. This is all the more relevant when it is
considered that many parameter detection systems perform very
delicate measurements. In iris recognition systems for example the
structure of the human iris is detected. In order to work properly
the system must be calibrated. A system may be calibrated at room
temperature and later on used outside at much lower or higher
temperatures. Systems with high temperature dependence of
refractive index will suffer from bad parameter detection
properties when the device is e.g. calibrated at room temperature
and used at substantially different temperatures.
SUMMARY OF THE INVENTION
[0028] The present invention provides a glass substrate that may be
used in a parameter detection systems that works reliably even at
markedly different temperatures.
[0029] In one embodiment the present invention is a glass substrate
having an average thickness of the glass substrate from 0.01 to 1.2
mm and having a temperature dependence of refractive index at a
wave-length of 850 nm in a temperature range from -40.degree. C. to
60.degree. C. of not more than 10.times.10.sup.-6/K.
[0030] In another embodiment the present invention is an infrared
band pass filter including a glass substrate and at least one
coating, the glass substrate having a thickness of 0.01 to 2 mm,
the glass substrate having a temperature dependence of refractive
index at a wavelength of 850 nm in a temperature range from
-40.degree. C. to 60.degree. C. of not more than
10.times.10.sup.-6/K, and the at least one coating having a
thickness of not more than 0.5 mm.
[0031] In yet another embodiment the present invention is an
infrared band pass filter having a glass substrate and at least one
coating, the glass substrate having a thickness of 0.01 to 2 mm,
the at least one coating having a thickness of not more than 0.5
mm, and the temperature dependent center wavelength drift in the
filter is less than 15 nm in a temperature range from -40.degree.
C. to 60.degree. C.
[0032] A desirable device should also exhibit beneficial
transmission properties, scratch resistance, filter proper-ties,
mechanical stabilities even at low thicknesses, low angle
dependency of optical properties, low manufacturing cost and
excellent hydrolytical and chemical stability. All these desirable
pre-requisites are met by the subject-matter described herein.
[0033] It has been found that the temperature dependence of
refractive index of the substrate in a coated filter used in a
parameter detection system should be as low as possible. The
present invention provides for systems, band pass filters and
substrates for band pass filters that allow for very reliable
operation of parameter detection systems at markedly different
temperatures.
[0034] The invention provides a parameter detection system
comprising: [0035] a) at least one light source capable of emitting
light in the direction of an object or person; [0036] b) at least
one band pass filter comprising a substrate and at least one
coating; [0037] c) optionally, at least one optical lens capable of
gathering light of the emitted wavelength; and [0038] d) at least
one image sensor positioned to receive light reflected from the
object or person; [0039] wherein the filter is positioned such that
light that is incident upon the lens and/or the image sensor must
pass through the filter before being gathered by the lens and/or
received by the image sensor; [0040] wherein the light emitted by
the light source is infrared light in a wavelength region of from
780 nm to 1,000 nm, preferably from 800 to 900 nm; [0041] wherein
the filter has a passband in a wavelength region of from 780 nm to
1,000 nm, prefer-ably from 800 to 900 nm; [0042] wherein the
substrate is made of glass and has a thickness of from 0.01 to 2
mm; wherein the coating has a thickness of not more than 0.5 mm;
and [0043] wherein the substrate has a temperature dependence of
refractive index at a wavelength of 850 nm in a temperature range
from -40.degree. C. to 60.degree. C. of not more than
10.times.10.sup.-6/K.
[0044] It has been found that parameter detection systems of the
kind outlined above show superior properties in terms of
temperature tolerance, i.e. the ability to work with substantially
the same efficacy at markedly different temperatures. The fact that
the substrate has a temperature dependence of refractive index at a
wavelength of 850 nm in a temperature range from -40.degree. C. to
60.degree. C. of not more than 10.times.10.sup.-6/K bestows the
filter used in the system with a good temperature tolerance. In
some embodiments, the temperature dependence of refractive index of
the substrate should be less than 8.times.10.sup.-6/K, more
preferably less than 6.times.10.sup.-6/K, more preferably less than
4.times.10.sup.-6/K and most preferably less than
2.5.times.10.sup.-6/K in a temperature range of from -40 to
+60.degree. C.
[0045] The temperature dependence of refractive index can be
measured easily by measuring the absolute refractive index of a
substrate at different temperatures. With regard to the temperature
values given above the value can easily be determined by measuring
the refractive index of the substrate at -40.degree. C. and at
60.degree. C., i.e. over a range of 100 K. For the substrates of
this invention the following is true:
(n.sub.850 nm/60.degree. C.-n.sub.850 nm/-40.degree. C.)/100
K=10.times.10.sup.-6/K or less (n=refractive index)
[0046] It has been found that the temperature dependent center
wavelength drift of the filter decreases when the temperature
dependence of refractive index is decreased in the substrate.
Preferably, the temperature dependent center wavelength drift in
the filter of the parameter detection system of this invention is
less than 15 nm, more preferably less than 10 nm and most
preferably less than 5 nm in a temperature range from -40.degree.
C. to 60.degree. C. The temperature dependent center wavelength
drift is measured by comparing the center wavelength of the
passband of the band pass filter at different temperatures. The
deviation of the center wavelength from the center wavelength at
room temperature, i.e. 20.degree. C., should not exceed the value
indicated above.
[0047] It has further been found that a higher temperature
dependence of refractive index will lead to undesirable
transmission losses in the filter when the ambient temperature is
markedly different from the temperature for which the system had
been optimized.
[0048] The light source used in the parameter detection system of
this invention may be a passive light source such as ambient light.
Generally, the light source may be any light source which emits
light in the desired wavelength region. An example of a passive
light source is the sun. In some embodiments, the light source is
an active light source, such as an LED.
[0049] The image sensor is preferably a sensor that is suitable to
measure the incoming light in a wavelength range of from 780 to
1,000 nm, preferably from 800 to 900 nm. In another embodiment, the
sensor is selected from a time-of-flight camera, a CCD or CMOS
sensor, or a combination thereof.
[0050] The optional lens may preferably be a lens made of glass. It
can be used to collect light that is reflected from the object or
person. The band pass filter, the light sensor and the optional
lens may be arranged in a housing. The light source may be arranged
in the same housing, or a different housing. The elements of the
system may be arranged in a device such as a portable device,
including a smart phone, a portable computer, a computer watch, or
a tablet computer. However, the system may also be arranged in
stationary devices such as gaming devices, TV sets, person-al
computers, intercommunication systems, home automation systems,
automotive security systems. The system may also be used in 3D
imaging systems with gesture control.
[0051] In particular, the system, filter and substrate of this
invention may be used in a number of devices, including but not
limited to smart phones, portable computers, computer watches,
tablet computers, gaming devices, TV sets, personal computers,
intercommunication systems, home automation systems, automotive
security systems, 3D imaging systems, gesture control systems,
touch sensors, fingerprint sensors, diagnostic systems, gaming
devices, interactive displays, 3D sensing systems, home appliances,
display devices, iris recognition systems and others. The system,
filter and substrate of this invention may be used for a number of
purposes including but not limited to iris recognition, 3D
scanning, interactive display, biometric detection or measurement
of biometric data, gesture control, gaming, fingerprint detection.
Components of such devices may include, but are not limited
thereto: optical or electrical interposers, thin film batteries,
illumination devices, particularly OLED or backlight units, PCBs or
other electronic wiring device, electronic passive component
(particularly capacitors), cover lenses, protective layers and/or
micro electro mechanical systems (MEMS)/micro opto mechanical
systems (MOEMS).
[0052] Parameter detection systems of this invention may be used to
detect a generally unlimited number of parameters. One prerequisite
however is that the parameter can be detected optically, using
infrared light. In some embodiments, the parameter to be detected
is a parameter pertaining to a human being. The parameter to be
detected may be selected from the iris structure of a human or
animal, the posture or movement of a human or animal, or biometric
data of a human or animal, such as iris structure. Biometric data
that can be detected, i.e. measured using the systems of this
invention include parameters pertaining to the face, hands, retina,
iris, signature, veins, or voice of a subject. The systems of this
invention can be used to analyze the facial characteristics of a
subject, the fingerprints, hand geometry, i.e. shape of the hand,
length of fingers, retina, i.e. analysis of capillary vessels at
the back of the eye, iris, veins, e.g. pattern of veins in the back
of the hand and the wrist.
[0053] This invention also relates to an infrared band pass filter
suitable for use in a parameter detection system according to this
invention. The filter comprising a substrate of glass and at least
one coating. The filter having a passband in a wavelength region of
from 780 nm to 1,000 nm, preferably from 800 to 900 nm, wherein the
substrate is made of glass and has an average thickness of from
0.01 to 2 mm, wherein the coating has a thickness of not more than
0.5 mm, and wherein the substrate has a temperature dependence of
refractive index at a wavelength of 850 nm in a temperature range
from -40.degree. C. to 60.degree. C. of not more than
10.times.10.sup.-6/K. Generally, the temperature dependence of
refractive index of the coating of the filter should be limited as
well. It is preferred that the respective value of the coating of
the filter is limited to values of less than 0.001/K, preferably
less than 12.times.10.sup.-6/K, preferably less than
10.times.10.sup.-6/K.
[0054] It has been found that it is beneficial when the temperature
dependence of refractive index of the substrate is similar to the
temperature dependence of refractive index of the coating.
Generally, the temperature dependence of refractive index of the
coating will be higher than that of the substrate. In some
embodiments, the ratio of temperature dependence of refractive
index of the coating to the temperature dependence of refractive
index of the substrate should not exceed 1,000, more preferably it
should not exceed 800, more preferably it should not exceed 500,
most preferably it should not exceed 100. The temperature tolerance
of the device will be increased if these values are observed.
[0055] The coating may comprise a plurality of layers. In some
embodiments the coating comprises from 10 to 1,000 layers,
preferably from 20 to 200 layers, more preferably from 30 to 80
layers.
[0056] The coating may be applied using a number of different
methods, including physical vapor deposition (PVD), chemical vapor
deposition (CVD), liquid phase deposition, ion beam sputtering
deposition, magnetron sputtering, plasma sputtering deposition,
thermal evaporation deposition, ion-assisted deposition, electron
beam gun evaporation, laser deposition, molecular beam epitaxial,
radio frequency heating (RF-heating) or sol-gel. Preferably,
thermal evaporation, ion beam sputtering, or plasma sputtering are
used as coating method. The coating serves the purpose of
reflecting portions of incident light that are not intended to pass
the filter. By using coatings to apply the desired pass band
properties to the filter, there are less restrictions with regard
to the optical properties of the glass as long as the glass has
sufficient transmission properties in the passband region.
[0057] Suitable coating materials are selected from inorganic and
organic coatings. Inorganic coatings are preferred because
inorganic coatings usually have better long term stability.
Preferred inorganic coating materials are selected from oxides and
fluorides. Preferred coating materials are selected from
Nb.sub.2O.sub.5, TiO.sub.2, Ta.sub.2O.sub.5, SiO.sub.2, MgF.sub.2,
Al.sub.2O.sub.3, HfO.sub.2 and ZnO.sub.2. All those coating
materials have a temperature dependence of refractive index of less
than 0.001/K. Preferred coating material that has a temperature
dependence of refractive index of less than 10.times.10.sup.-6/K
are selected from SiO.sub.2, MgF.sub.2, Al.sub.2O.sub.3 and
HfO.sub.2.
[0058] This invention further relates to a glass substrate suitable
for use in an infrared band pass filter according to this
invention, wherein the glass substrate has a transmission more than
90% at a thickness of 10 mm in the wavelength region of from 780 to
1000 nm, preferably from 800 to 900 nm, and wherein the glass
substrate has a temperature dependence of refractive index at a
wave-length of 850 nm in a temperature range from -40.degree. C. to
60.degree. C. of not more than 10.times.10.sup.-6/K.
[0059] The glass substrate of this invention has a transmission of
more than 90%, preferably more than 95% in the wavelength region of
from 780 to 1000 nm, preferably in the region of from 800 to 900
nm, at a thickness of 10 mm. Good transmission of the filter
substrate is important because any losses of transmission must be
compensated for by using higher initial light intensities, which
will affect the S/N ratio and lead to higher power consumption of
the systems used and might even lead to harmful light intensities
in certain applications.
[0060] The glass that is used as the substrate in this invention
preferably has a Knoop hardness HK0.1/20 of more than 450.
Sufficient hardness of the substrate is important because it will
increase the overall product lifetime and avoid the formation of
scratches on the surface of the filter. Scratches lead to undesired
reflections and thus to a decrease in detection efficacy. Usually,
very high hardness is not desired in filter substrates because high
hardness makes polishing expensive. However, since the glasses of
this invention can be produced with excellent surface properties
without polishing, the high hardness value does not have a drawback
for these glasses.
[0061] In the Knoop hardness test the indentation depth of a
rhombus-shaped diamond pressed with a defined force and time on the
material is measured. The diamond surfaces have defined
intersection angles of 172.5.degree. and 130.0.degree.. During
pressing of the diamond into the glass plate an elastic and plastic
deformation occurs. The size of the permanent indentation depends
on the hardness of the material, which is given by the chemical
composition. The Knoop hardness can be calculated from the diagonal
size d of the indentation using the following formula:
HK=1.4233.times.F/d.sup.2
[0062] The standard ISO 9385:1990 describes the measurement
procedure for glasses. In accordance with this standard, the values
for Knoop hardness HK are listed in the data sheets for a test
force of 0.9807 N (corresponds to 0.1 kp) and an effective test
period of 20 s. The test was performed on polished glass surfaces
at room temperature. The data for hardness values are rounded to 10
HK 0.1/20. The microhardness is a function of the magnitude of the
test force and decreases with increasing test force.
[0063] The glass of the substrate used in this invention preferably
has an average thickness of from 0.01 to 1.2 mm, preferably from
0.1 to 0.7 mm, most preferably up to 0.5 mm. The glass used in this
invention can be produced in very thin shape. Particularly, the
glass can be produced very economically using drawing methods, such
as redraw, down draw or overflow fusion; alternatively float
processes can be used.
[0064] The invention also includes a method of detecting at least
one parameter, including the steps of: [0065] a. illuminating a
subject or an object of interest using light within a wavelength
range of from 780 to 1,000 nm, preferably from 800 to 900 nm;
[0066] b. measuring at least one property of the light reflected
from the subject or object of interest in a wavelength range of
from 780 to 1,000 nm, preferably from 800 to 900 nm; wherein before
the at least one property of the light is measured, the light
passes through at least one infrared band pass filter, the band
pass filter comprising a substrate of glass and at least one
coating, the filter having a passband in a wavelength region of
from 780 nm to 1,000 nm, preferably from 800 to 900 nm, wherein the
substrate is made of glass and has a thickness of from 0.01 to 2
mm, wherein the coating has a thickness of not more than 0.5 mm,
and wherein the substrate has a temperature dependence of
refractive index at a wave-length of 850 nm in a temperature range
from -40.degree. C. to 60.degree. C. of not more than
10.times.10.sup.-6/K.
[0067] It has been found that when a glass is used as the substrate
of the filter in the systems of this invention, a high leaching
tendency will lead to decreased product lifetime and inconsistent
measuring results. Therefore, it is desirable that the leaching
properties of the glass used as the substrate are decreased.
Preferably, the glass has an HGB1 according to ISO719.
[0068] So that uniform results can be obtained the substrate glass
should have a very smooth surface. In some embodiments, the RMS
roughness of the glass substrate is less than 5 nm, preferably less
than 1 nm RMS.
[0069] The coefficient of thermal expansion (CTE) of the glass
should not deviate too much from the respective CTEs of the coating
layers. It has been proven advantageous to use a glass having a CTE
of at least 2.times.10.sup.-6/K and not more than
11.times.10.sup.-6/K. Preferably, the CTE is at least
5.times.10.sup.-6/K and less than 8.5.times.10.sup.-6/K. Glass
compositions that are preferably used in this invention will be
described in the following.
[0070] Glasses used in this invention are characterized by certain
compositional ranges. In this description we refer to the cationic
compositions of the glasses. In these compositions--if nothing else
is indicated--"silicon" refers to Si.sup.4+, "boron" refers to
B.sup.3+, "aluminum" refers to Al.sup.3+, "lithium" refers to
Li.sup.+, "sodium" refers to Na.sup.+, "potassium" refers to
K.sup.+, "magnesium" refers to Mg.sup.2+, "calcium" refers to
Ca.sup.2+, "barium" refers to Ba.sup.2+, "zinc" refers to
Zn.sup.2+, "titanium" refers to Ti.sup.4+, "zirconium" refers to
Zr.sup.4+, "arsenic" refers to the sum of As.sup.3+ and As.sup.5+,
"antimony" refers to the sum of Sb.sup.3+ and Sb.sup.5+, "iron"
refers to the sum of Fe.sup.3+ and Fe.sup.4+, "cerium" refers to
the sum of Ce.sup.3+ and Ce.sup.4+, "tin" refers to the sum of
Sn.sup.2+ and Sn.sup.4+, and "sulfur" relates to the total amount
of sulfur in all its valence states and oxidation levels.
[0071] The glasses that are suitable for the filter substrate of
the present invention have certain preferred composition that will
be outlined below. The glasses generally comprise cationic and
anionic components. The composition of cations in the glass will be
given in cationic percentages (cat.-%), i.e. indicating the molar
proportion of the respective cation relative to the total molar
amount of cations in the composition. Preferably, the glasses
comprise the following components, in cat.-%, based on the total
molar amount of cations in the glass: silicon 40 to 75 cat.-%,
boron 0 to 23 cat.-%, aluminum 0 to 20 cat.-%, lithium 0 to 18
cat.-%, sodium 0 to 25 cat.-%, potassium 0 to 15 cat.-%, magnesium
0 to 10 cat.-%, calcium 0 to 9 cat.-%, barium 0 to 4 cat.-%, zinc 0
to 7 cat.-%, titanium 0 to 5 cat.-%, zirconium 0 to 3 cat.-%. In
some embodiments, the cations in the glasses consist of the cations
mentioned in the before-mentioned list to an extent of at least
95%, more preferably at least 97%, most preferably at least 99%. In
most embodiments, the cationic components of the glass essentially
consists of the mentioned cations.
[0072] As anionic components the glass preferably comprises at
least one anion selected from fluorine (F.sup.-), oxygen
(O.sup.2-), chloride (Cl.sup.-). Most preferably, the anions
present in the glass consist of oxygen to an extent of at least
95%, more preferably at least 97%, most preferably at least 99%. In
most preferred embodiments, the anionic component of the glass
essentially consists of oxygen.
[0073] A particular glass composition comprises the following
components, in cat.-%, based on the total molar amount of cations
in the glass: silicon 48 to 60 cat.-%, boron 10.5 to 15.5 cat.-%,
aluminum 2 to 8.5 cat.-%, sodium 8 to 14 cat.-%, potassium 5.5 to
13.5 cat.-%, zinc 2 to 6, titanium 1 to 5 cat.-%. In some
embodiments, the cations in the glasses consist of the cations
mentioned in the before-mentioned list to an extent of at least
95%, more preferably at least 97%, most preferably at least 99%. In
most embodiments, the cationic components of the glass essentially
consists of the mentioned cations.
[0074] Another particular glass composition comprises the following
components, in cat.-%, based on the total molar amount of cations
in the glass: silicon 45 to 60 cat.-%, aluminum 14 to 20 cat.-%,
sodium 15 to 25 cat.-%, potassium 1.5 to 8.5 cat.-%, magnesium 2 to
9, zirconium 0.1 to 1.3 cat.-%, cerium 0.01 to 0.3 cat.-%. In some
embodiments, the cations in the glasses consist of the cations
mentioned in the before-mentioned list to an extent of at least
95%, more preferably at least 97%, most preferably at least 99%. In
most embodiments, the cationic components of the glass essentially
consists of the mentioned cations.
[0075] The terms "X-free" and "free of component X", respectively,
as used herein, refer to a glass, which essentially does not
comprise said component X, i.e. such component may be present in
the glass at most as an impurity or contamination, however, is not
added to the glass composition as an individual component. This
means that the component X is not added in essential amounts.
Non-essential amounts according to the present invention are
amounts of less than 100 ppm, preferably less than 50 ppm and more
preferably less than 10 ppm. Thereby "X" may refer to any
component, such as lead cations or arsenic cations. Preferably, the
glasses described herein do essentially not contain any components
that are not mentioned in this description.
[0076] The matrix of the glass comprises silicon in proportions of
40 to 75 cat.-%. Silicon is an important network former in the
glass matrix which is very important for the glass properties. In
particular, silicon cations are important for the chemical
resistance, hardness and scratch resistance of the glass. In most
embodiments the glasses comprise at least 43 cat.-% of silicon,
more preferably at least 45 cat.-% of silicon, still more
preferably at least 47.5 cat.-% of silicon, and most preferably at
least 48 cat.-% of silicon. However, contents of silicon cations
which are too high may result in an increase of the glass
transition temperature, making glass production uneconomical.
Therefore, it is particularly preferable that the content of
silicon cations is at most 75 cat.-%, further preferable at most 70
cat.-%, still more preferable at most 65 cat.-%, and most
preferable at most 60 cat.-%.
[0077] Besides silicon cations the glass also comprises at least
one second network former. The glasses contain boron cations as an
additional network former in proportions of 0 to 23 cat.-%. Through
its network forming properties boron cations essentially support
the stability of the glass. In the case of contents of boron
cations which are too low, the required stability in the glass
system cannot be guaranteed. In some embodiments the glasses
comprise at least 0 cat.-% of boron, more preferably at least 5
cat.-% of boron, still more preferably at least 7.5 cat.-% of
boron, and most preferably at least 10.5 cat.-% of boron.
Nevertheless, in the case of contents of boron cations in the glass
which are too high the viscosity may be reduced strongly so that a
reduction of the crystallization stability has to be accepted.
Therefore, it is particularly preferable that the content of boron
cations is at most 23 cat.-%, further preferable at most 20 cat.-%,
still more preferable at most 18 cat.-%, and most preferable at
most 15.5 cat.-%.
[0078] In the glasses preferably the sum of silicon and boron
cations cat.-% is from 40 to 95. In some embodiments the sum of
silicon and boron cations cat.-% in the glasses is at least 45
cat.-%, more preferably at least 48 cat.-%, still more preferably
at least 50, and most preferably at least 60 cat.-%. It is
particularly preferable that the sum of silicon and boron cations
cat.-% in the glasses is at most 95 cat.-%, further preferable at
most 85 cat.-%, still more preferable at most 75.0 cat.-%, and most
preferable at most 72 cat.-%.
[0079] It has been found that the temperature dependence of
refractive index is influenced by the network formers aluminum,
silicon and boron in the glass. Therefore, the glasses show a ratio
of the sum of aluminum and boron relative to the amount of silicon
in cationic percentages of from 0 to 1. Preferably, this ratio is
from >0 to 0.8, more preferably from >0.25 to 0.6, most
preferably from 0.3 to 0.4.
[0080] In the glasses preferably aluminum cations are contained in
proportions of 0 to 20 cat.-%. The addition of aluminum cations
results in improved glass forming properties and generally supports
the improvement of chemical resistance. In some embodiments the
glasses comprise at least 0 cat.-% of aluminum, more preferably at
least 1 cat.-% of aluminum, still more preferably at least 2 cat.-%
of aluminum, and most preferably at least 3 cat.-% of aluminum.
However, contents of aluminum cations which are too high result in
an increased tendency to crystallization. Therefore, it is
particularly preferable that the content of aluminum cations is at
most 20 cat.-%, further preferable at most 15 cat.-%, still more
preferable at most 10 cat.-%, and most preferable at most 8
cat.-%.
[0081] The glasses preferably contain fluxing agents to improve
melting properties, particularly comprising alkali metal cations
and/or alkaline earth metal cations. Preferably, the sum of fluxing
agents .SIGMA.{.SIGMA.R.sup.2+ (R=Mg, Ca, Sr, Ba)+.SIGMA.R.sup.+
(R'=Li, Na, K)} preferably is 5 to 40 cat.-%. In some embodiments
the sum of the amounts of the fluxing agents in the glasses is at
least 5 cat.-%, more preferably at least 7 cat.-%, still more
preferably at least 12 cat.-%, and most preferably at least 15
cat.-%. If the amount of fluxing agents in the glass is too high,
chemical resistance will decrease. It is particularly preferable
that the sum of the fluxing agents in the glasses is at most 35
cat.-%, further preferable at most 30 cat.-%, still more preferable
at most 25 cat.-%, and most preferable at most 23 cat.-%.
[0082] Alkali metal cations improve the meltability of the glass
and thus allow an economic production. Also, they may are necessary
for allowing chemical strengthening of the glass by ion exchange
treatment. During the production of the glass the alkali metal
cations serve as fluxing agents. The sum of the amounts of the
alkali metal cations lithium, sodium and potassium in the glasses
preferably is 0 to 35 cat.-%. In some embodiments the sum of the
alkali metal cations is at least 5 cat.-%, more preferably at least
7 cat.-%, still more preferably at least 10 cat.-%, and most
preferably at least 15 cat.-%. However, if contents of alkali metal
cations are too high the weathering resistance of the glass may be
compromised and thus the range of applications thereof may strongly
be limited. Therefore, it is particularly preferable that the sum
of the alkali metal cations is at most 35 cat.-%, further
preferable at most 30 cat.-%, still more preferable at most 25
cat.-%, and most preferable at most 23 cat.-%.
[0083] In the glasses preferably lithium cations are contained in
proportions of 0 to 18 cat.-%. Lithium serves as a fluxing agent
and has excellent properties for ion exchange strengthening.
However, lithium affects chemical stability of the glasses to a
great extent so that its content should be limited. It is
particularly preferable that the content of lithium cations is at
most 18 cat.-%, further preferable at most 10 cat.-%, still more
preferable at most 3 cat.-%, and most preferable at most 1 cat.-%.
In some embodiments the glasses are free of lithium cations.
[0084] In the glasses preferably sodium cations are contained in
proportions of 0 to 25 cat.-%. Sodium is a good component for ion
exchange treatment. But, as with all alkali metal ions the amount
of this component should not be too high because it decreases
chemical stability. In some embodiments the glasses comprise at
least 3 cat.-% of sodium, more preferably at least 5 cat.-% of
sodium, still more preferably at least 8 cat.-% of sodium, and most
preferably at least 9 cat.-% of sodium. It is particularly
preferable that the content of sodium cations is at most 23 cat.-%,
further preferable at most 22 cat.-%, still more preferable at most
20 cat.-%, and most preferable at most 15 cat.-%.
[0085] In the glasses preferably potassium cations are contained in
proportions of 0 to 15 cat.-%. The negative impact of potassium on
chemical stability is less strong compared to the other alkali
metal ions. However, potassium is not suitable for ion exchange
treatment. Also, the content of potassium is preferably limited
because it contains isotopes that emit beta rays. In some
embodiments the glasses comprise at least 1 cat.-% of potassium,
more preferably at least 2 cat.-% of potassium, still more
preferably at least 3 cat.-% of potassium, and most preferably at
least 5.5 cat.-% of potassium. It is particularly preferable that
the content of potassium cations is at most 15 cat.-%, further
preferable at most 13 cat.-%, still more preferable at most 12
cat.-%.
[0086] It has been found that the leaching tendency of the
substrate glass can be reduced by using both sodium and potassium
in the glass and keeping the ratio of sodium to potassium in cat.-%
in a range of up to 5, more preferably up to 4.5, more preferably
up to 3.5, preferably up to 2.0 and most preferably at less than
1.6. Keeping this ratio low, i.e. the sodium does not exceed a
certain amount relative to the amount of potassium, provides for
glasses having good meltability and excellent chemical and
hydrolytical resistance. Specifically, such glasses will have an
HGB1 according to ISO 719:1989. However, in order to adjust the
viscosity in the melt to a desirable value, the ratio of sodium to
potassium should be more than 0.5, preferably more than 0.7 and
most prefer-ably at least 0.8.
[0087] Alkaline earth metal cations improve the meltability of the
glass and thus allow for an economic production. During the
production of the glass they serve as fluxing agents. The sum of
the alkaline earth metal cations magnesium, barium and calcium in
the glasses preferably is of 0 to 15 cat.-%. Alkaline earth metal
ions affect chemical resistance of the glass with little positive
effects in terms of ion exchange treatment. Hence, in this
invention the glasses do preferably not comprise any alkali earth
metal ions. It is particularly preferable that the sum of the
alkali earth metal cations in the glasses is at most 13 cat.-%,
further preferable at most 10 cat.-%, still more preferable at most
5 cat.-%, and most preferable at most 1 cat.-%. In some embodiments
the glasses are free of alkali earth metals. Moreover, alkaline
earth metal cations and zinc cations may be used to adjust the
viscosity of the glasses, particularly the fine tuning of the
viscosity-temperature profile. Moreover, alkaline earth metal
cations and zinc cations--as alkali metal cations--may be used as
fluxing agents. The glasses are preferably free of at least one
cation selected from the group comprising magnesium cations,
calcium cations, strontium cations, barium cations and zinc
cations. Preferably, the glasses are free of magnesium cations,
calcium cations, strontium cations and barium cations.
[0088] In the glasses preferably magnesium cations are contained in
proportions of 0 to 10 cat.-%. It is particularly preferable that
the content of magnesium cations is at most 8 cat.-%, more
preferably at most 6 cat.-%. In some embodiments the glasses are
free of magnesium. In the glasses preferably calcium cations is
contained in proportions of 0 to 9 cat.-%. It is particularly
preferable that the content of calcium cations is at most 8 cat.-%,
further preferable at most 3 cat.-%. In some embodiments the
glasses are free of calcium. In the glasses preferably barium
cations are contained in proportions of 0 to 4 cat.-%. It is
particularly preferable that the content of barium cations is at
most 4 cat.-%, further preferable at most 3 cat.-%, still more
preferable at most 2 cat.-%, and most preferable at most 1 cat.-%.
In some embodiments the glasses are free of barium. In some
embodiments the glasses are free of strontium.
[0089] In the glasses preferably zinc cations are contained in
proportions of 0 to 7 cat.-%. Zinc cations may be contained in the
glass as an additional fluxing agent as well as for adjusting the
melting point in a targeted manner. By the addition of the network
modifier zinc the melting point of glass may be reduced. In some
embodiments the glasses comprise at least 1 cat.-% of zinc, more
preferably at least 2 cat.-% of zinc, still more preferably at
least 3 cat.-% of zinc. However, contents of zinc cations which are
too high may result in a reduction of the melting point of the
glasses. It is particularly preferable that the content of zinc
cations is at most 6 cat.-%, further preferable at most 5
cat.-%.
[0090] In the glasses preferably titanium cations are contained in
proportions of 0 to 5 cat.-%. Titanium cations are added to the
glasses for improving their optical properties. In particular, with
the addition of titanium, the refractive index of the glasses can
be adjusted in a targeted manner. The refractive index increases
with an increasing content of titanium cations of the glass. The
addition of titanium cations is connected with a further advantage
where the UV edge of the transmittance spectrum of the glass is
shifted to higher wave lengths, wherein this shift is higher, when
more titanium is added. In some embodiments the glasses comprise at
least 0.1 cat.-% of titanium, more preferably at least 0.5 cat.-%
of titanium, still more preferably at least 1 cat.-% of titanium,
and most preferably at least 2 cat.-% of titanium. However,
contents of titanium cations which are too high may result in
undesirable crystallization of the glass. Titanium cations may
increase the refractive index of the glasses. Particularly together
with zirconium cations, titanium cations may deteriorate
transmission in the blue spectral range and thus may shift the
UV-edge into the longer wave lengths. Therefore, it is particularly
preferable that the content of titanium is at most 5 cat.-%,
further preferable at most 4 cat.-%.
[0091] In the glasses preferably zirconium cations are contained in
proportions of 0 to 3 cat.-%. Zirconium cations may be used to
adjust the refractory index of the glasses. However, a content of
zirconium cations, which is too high, may decrease the meltability
and particularly may lead to stronger crystallization of the
glasses. It is particularly preferable that the content of
zirconium is at most 2 cat.-%, further preferable at most 1 cat.-%,
still more preferable at most 0.5 cat.-%. In some embodiments the
glasses are free of zirconium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0092] The above mentioned and other features and advantages of
this invention, and the manner of attaining them, will become more
apparent and the invention will be better understood by reference
to the following description of an embodiment of the invention
taken in conjunction with the accompanying drawing, wherein:
[0093] FIG. 1 shows a transmission spectrum of a substrate glass of
this invention.
[0094] The exemplifications set out herein illustrate embodiments
of the invention and such exemplifications are not to be construed
as limiting the scope of the invention in any manner.
DETAILED DESCRIPTION OF THE INVENTION
Examples
[0095] Example glass substrates and example filters were prepared
and some properties were measured. The glass compositions tested
can be seen in table 1 below.
Composition Examples
[0096] The following table 1 shows exemplary glass compositions in
cat.-% that are useful as substrate glasses in the compositions of
this invention. The glasses shown in table 1 contained only oxides
as the anionic component, i.e. the glasses were oxidic.
TABLE-US-00001 TABLE 1 Glass 1 2 3 4 5 6 7 8 9 10 11 12 silicon 55
52 65 65 57 50 48 70 60 56 54 49 boron 16 13 14 1 20 15 3 aluminum
19 17 4 6 17 2 6 14 13 13 lithium 16 <1 sodium 21 19 15 11 10 14
7 16 22 18 24 potassium 5 6 10 8 11 <1 <1 2 7 5 magnesium 4 5
5 8 3 calcium 5 8 7 <1 3 <1 <1 2 barium 1 <1 1 zinc 2 3
4 5 <1 titanium <1 <1 3 3 zirconium <1 2 <1 <1
<2 arsenic <1 antimony <1 <1 <1 <1 <1 <1
cerium <1 <1 iron <1 <1 <1 <1 sulfur <0.6 tin
<1 <1 Na/K -- >4 >3 >1 >1 <1 >14 >7 --
>11 >2 >4 (Al + B)/Si 0.6 0.3 0 0 0.3 0.4 0.4 0.3 0.35
0.25 0.25 0.3
[0097] The compositions above are the final compositions measured
in the glass. The skilled person knows how to obtain these glasses
by melting the necessary raw materials.
[0098] Producing Glass Substrate
[0099] Glasses were produced using suitable raw materials to obtain
the final compositions shown in table 1. Raw materials were melted
in a melting crucible. After melting the glass was formed into thin
glass articles having thicknesses of about 0.3 mm.
[0100] All of the glasses disclosed above could be produced using
the down draw method. The down draw method is as such known to the
skilled person. This method is a very economical way of producing
thin glass articles. Not every glass can be produced into thin
glass articles with the down draw method. It is one advantage of
the glasses used in this invention that the glass compositions can
be processed in the down draw process. An alternative method that
can be used as well is the overflow fusion method which is also
known to the skilled person.
[0101] Alternatively, the glasses can also be processed using the
redraw method as, for example as described in US 2015/0274573 A1,
or US 2014/0357467 A1.
[0102] The temperature dependence of refractive index was measured
in the glasses of table 1. For conducting this measurement the
following steps were taken. First, the refractive index at
-40.degree. C. was measured. Second, the refractive index at
60.degree. C. was measured. Then the temperature dependence of
refractive index was calculated using the following formula:
(n.sub.850 nm/60.degree. C.-n.sub.850 nm/-40.degree. C.)/100
K=10.times.10.sup.-6/K or less (n=refractive index)
[0103] After producing the glass and forming a thin substrate,
coatings were applied to the substrate in order to produce an IR
band pass filter. A total of 40 coating layers were applied. The IR
band pass filter had beneficial properties, including very good
transmission in the pass band wave-length region, and good
temperature tolerance.
[0104] While this invention has been described with respect to at
least one embodiment, the present invention can be further modified
within the spirit and scope of this disclosure. This application is
therefore intended to cover any variations, uses, or adaptations of
the invention using its general principles. Further, this
application is intended to cover such departures from the present
disclosure as come within known or customary practice in the art to
which this invention pertains and which fall within the limits of
the appended claims.
* * * * *